According to Art. 115 EPC a third party does not become a party to the proceedings. The third party, not being a party to proceedings, does not enjoy the right to be heard by the EPO. The observations were to be examined as submitted and assessed with regard to credibility (T 951/93, T 1196/08).
In T 951/91 the board found that by interpreting Art. 115 EPC 1973 in the light of their object and purpose, it was clear that they were intended exclusively to cut down, and not to extend, the rights of third parties, still less to extend their rights beyond the rights of parties to the EPO.
As a third party within the meaning of Art. 115 EPC is not a party to the proceedings and has no more than an opportunity to "present observations", the admissibility of these observations is entirely a matter for the board. While it is well-established by case-law that thirdparty observations can be considered, both at first instance and on appeal, there is no obligation on the board beyond such consideration and no right of a third party to be heard on the admissibility of its observations or any evidence in support of them. The actual parties to proceedings naturally have the right to be heard in relation to such observations, but their admissibility is entirely a matter for the board (T 390/07).
In T 283/02, the opposition division had duly forwarded the observations by third parties to the patentee, who had made no comment. The failure of the opposition division to mention these observations in its decision did not constitute a procedural violation, even though a mention would have been desirable.